For example, there are transmission devices on which a plurality of communication cards are mounted and that transmit communication signals via each of the communication card. FIG. 8 is a diagram illustrating an example of a transmission device. A transmission device 100 illustrated in FIG. 8 has mounted thereon a plurality of interface (IF) card 110 and a control card 120 that controls each of the IF cards 110. Each of the IF cards 110 is, for example, a card that manages communication interfaces with a transmission network. The transmission device 100 has mounted thereon, for example, five IF cards 110 indicated by #1 to #5. Each of the IF cards 110 contains therein a central processing unit (CPU) 110A that controls the corresponding IF card 110 itself. Furthermore, the control card 120 contains therein a CPU 120A that controls the control card 120 itself. The transmission device 100 connects with a host PC 130 that controls the transmission device 100 and acquires time information or setting information from the host PC 130.
The control card 120 in the transmission device 100 acquires set time information that includes therein set time from the host PC 130 at a periodical time zone, for example, once a day; sets, in an internal timer that is used as a clock of its own card, the set time included in the acquired set time information; and reflects the set time. Namely, the CPU 120A in the control card 120 sets the set time in the internal timer and starts, from the set time, a time measuring operation of the internal timer. Furthermore, the control card 120 distributes the set time information acquired from the host PC 130 to each of the IF cards 110 in the transmission device 100 by using multicast transmission.
Each of the IF cards 110 sets, in the internal timer that is used as a clock of its own card, the set time included in the set time information received from the control card 120 and reflects the set time. Namely, each of the CPUs 110A in the corresponding IF cards 110 sets the set time in the corresponding internal timer and starts a time measuring operation of the corresponding internal timer from the set time. Consequently, by setting the set time included in the set time information acquired from the host PC 130 in the internal timers in the control card 120 and the IF cards 110 and by reflecting the set time, the transmission device 100 ensures synchronization of measured time among CPUs 110A (120A) in the cards.    Patent Document 1: Japanese Laid-open Patent Publication No. 05-300113    Patent Document 2: Japanese Laid-open Patent Publication No. 2005-303761
However, as illustrated in FIG. 9, processing loads of the CPUs 110A in the IF cards 110 in the transmission device 100 differ depending on specifications of the CPUs 110A themselves or the content of the processes performed by the CPUs 110A. Accordingly, even when each of the CPUs 110A in the corresponding IF cards 110 receives set time information from the control card 120, there may be a case in which, depending on a processing state, the CPU 110A is not able to immediately set the set time included in the received set time information in the internal timer and reflect the set time. Namely, in the CPU 110A in each of the IF cards 110, because there is a variation in the time period for which the set time included in the set time information is reflected to the internal timer, an error occurs in the measured time in the subject internal timer within the range between, for example, few millisecond and one second.
Furthermore, the CPU 110A in each of the IF cards 110 receives set time information received from the control card 120; however, as illustrated in FIG. 9, the reception timing of the set time information differs in accordance with a traffic state of the communication path. Accordingly, in the CPU 110A in each of the IF cards 110, because there is a variation, depending on the reception timing of the set time information, in the time period for which the set time included in the received set time information is reflected to the internal timer, an error occurs in the measured time of the subject internal timer.
Furthermore, when the CPU 110A in each of the IF cards 110 detects a failure, the CPU 110A in each of the IF cards 110 has a function of notifying the control card 120 of the failure content and the occurrence time of that failure. At this time, the CPU 110A in each of the IF cards 110 acquires the occurrence time of the failure by using the measured time of the internal timer.
However, because an error is present in the measured time of the internal timer among the IF cards 110 in the transmission device 100, when the occurrence time of the failure is collected from each of the IF cards 110, the control card 120 is not able to identify the accurate occurrence time of the failure.